The invention relates to devices for delivering, administering, injection, dispensing or infusing substances, and to methods of making and using such devices. More particularly, it relates to a dose metering mechanism with a multiple anti-rotation locking system and a device for administering an injectable product, which enable a dose to be freely selected by a user of the device. The injection device is particularly suitable for applications where the user self-administers the product and is able to select, i.e. set or choose, the dose individually with every administration. In some preferred embodiments, the device is an injection device of the type used for administering insulin as a diabetic treatment, or for administering growth hormone.
Patent specification EP 0 713 403 A1 discloses a syringe for administering liquid pharmaceutical mixtures and generally also other liquids, which allows a dose of liquid to be administered per injection to be set once. Specifically, a setting is made by a pharmacist. However, in the case of a patient who then has to self-administer the pharmaceutical liquid with the syringe, it is difficult to change the dose, once it has been set. The intention is to prevent an incorrect dose from being administered with the syringe. A syringe of this type is not entirely satisfactory for all uses because in some treatment regimes, an optimum dose varies depending, for example, on the time of day, sporting activities or the consumption of meals.
Injection devices which satisfy the need for variable doses or dosing are known from patent specifications WO 97/36625 and DE 199 00 792 C2, for example. These two specifications relate to injection devices, each of which has a conveying mechanism for dispensing the product, and a dose metering mechanism for setting the product dose which can be conveyed and hence dispensed by the conveying device during a subsequent injection. The conveying mechanism comprises a plunger, the forward stroke of which conveys the product from a product reservoir, a plunger rod and a drive member for the plunger rod. The drive member and the plunger rod engage with one another so that a forward movement of the drive member causes the plunger rod to move in the same way but the drive member performs a reverse movement in the opposite direction until it reaches a trigger position, from which another injection can be initiated. The trigger position is determined by means of the dose metering mechanism, which forms an adjustable dose setting stop for the drive member. Although the known devices have proved to be efficient in practice, they could still be improved to make them more reliable in terms of ruling out the risk of incorrect doses.
Patent specification EP 0 879 610 B1 discloses a re-usable dispensing mechanism for medicaments. A projection mounted on the housing of the device engages in one of several grooves adapted to the projection, disposed on a selection element. The projection is resiliently attached to the housing so that when the housing is turned towards the selection element, the selection element springs out of one groove into an adjacent groove, thereby making an audible clicking sound.